Compounds of oxygen - Practice Questions & MCQ

Preparation
Dioxygen can be obtained in the laboratory by the following ways:

• By heating oxygen containing salts such as chlorates, nitrates and permanganates.
  
• By the thermal decomposition of the oxides of metals low in the electrochemical series and higher oxides of some metals.
  
• Hydrogen peroxide is readily decomposed into water and dioxygen by catalysts such as finely divided metals and manganese dioxide.
  
  On large scale it can be prepared from water or air. Electrolysis of water leads to the release of hydrogen at the cathode and oxygen at the anode.

Properties
Dioxygen is a colourless and odourless gas. Its solubility in water is to the extent of 3.08 cm³ in 100 cm³ water at 293 K which is just sufficient for the vital support of marine and aquatic life. It liquefies at 90 K and freezes at 55 K. Oxygen atom has three stable isotopes: ¹⁶O, ¹⁷O and ¹⁸O. Molecular oxygen, O₂ is unique in being paramagnetic inspite of having even number of electrons. Dioxygen directly reacts with nearly all metals and non-metals except some metals ( e.g., Au, Pt) and some noble gases. Its combination with other elements is often strongly exothermic which helps in sustaining the reaction. However, to initiate the reaction, some external heating is required as bond dissociation enthalpy of oxgyen-oxygen double bond is high (493.4 kJ mol^–1).

Uses

• It is used in oxyacetylene welding.
• In the manufacture of many metals, particularly steel.
• Oxygen cylinders are widely used in hospitals, high altitude flying and in mountaineering.
• The combustion of fuels, e.g.,hydrazines in liquid oxygen, provides tremendous thrust in rockets.